1. Field of the Invention
The present invention relates to an optical fiber and, more particularly, to an optical fiber for an optical amplifier which is configured to perform optical signal amplification by a rare earth element doped into the optical fiber and optical signal amplification by a non-linear Raman effect of a core composition material, in which the optical amplification band by the rare earth elements and the optical amplification band by the Raman effect simultaneously occur or have different bands not to overlap.
2. Discussion of Related Art
In general, a Raman optical amplifier and an erbium-doped fiber amplifier (EDFA) have been widely researched as an amplifier which is very important in a wavelength division multiplex (WDM) optical communication system with development of a high power semiconductor laser diode.
The EDFA can perform amplification of more than 80 nm due to development of L-band amplification as well as C-band amplification. However, the EDFA which can perform S-band amplification has been attempted but is not commercialized yet. There was an attempt to amplify an S-band by arranging a C-band reduction filter in the EDFA. However, the S-band EDFA is too low in final optical output power and so it was not put to practical use. For these reasons, the Raman optical amplifier has been suggested as an alternative for the S-band.
The Raman optical amplifier has a gain region depending on a pumping wavelength and thus can amplify a band which the EDFA cannot amplify. The Raman optical amplifier can extend a gain bandwidth by more than 100 nm by multi-wavelength pumping, and a distributed type Raman optical amplifier which uses a transmission medium as an amplification medium can greatly improve an optical signal to noise ratio (OSNR). On the contrary, the Raman optical amplifier has disadvantage in that it needs an optical fiber for non-linear optical amplification which is relatively long.